My neighbor was selling his Corvette, less than 12k miles, and I was considering it. It was mint, a real garage queen he bought new and almost never drove. It really looked like it had never even been sat in. Took it out to the interstate and opened it up to about 100 mph for a very short burst, drove around town a while and headed back. Went back to his house, popped the hood, talked a while, and then I glanced at the tires, sitting there all nice and shiny with plenty of tread.....they were the original factory tires. "Plenty of tread, they're in great shape, wont need to replace those for a while!". Oh boy...The Vette was a '92. It was currently 2011. I immediately broke out into a sweat knowing I had just driven a Vette at 100 mph on 19 year old tires.
Told him to knock a grand off for new tires or he can replace them himself first. He wouldnt budge, told me I was nuts. I bought a newer Vette a few days later, then about a week after that he called me and said you win, several of the local tires stores gave him a stern lecture, so he replaced them and we were good to go. Had to break the news to him.